Transformer with regulatable leakage reactance



Mai'ch 2, 1948. E. FRIES 2,437,021

TRANSFORMER WITH REGULATABLE LEAKAGE REACTANCE Filed Oct. 6, 1945 2Sheets-Sheet l March 2, 1948. E. FRIES 2,437,021

TRANSFORMER WITH REGULATABLE LEAKAGE REACTANCE Filed Oct. 6, 1945 2Sheets-Sheet 2 Patented Mar. 2, 1948 TRANSFORMER WITH REGULATABLELEAKAGE REACTANCE Eduard Fries, Zurich-Oerlikon, Switzerland ApplicationOctober 6, 1945, Serial No. 620,731 Claims. (Cl. 171-777) The inventionrelates to transformers with variable reactance and while not limitedthereto is particularly applicable to welding transformers I whosesecondary reactance must be varied within wide limits.

My copending application, Serial Number 490,- 787, filed June 14, 1943,Patent No. 2,411,370 granted November 19, 1946 discloses a transformerhaving a closed primary magnetic core provided with primary windings andsecondary windings telescoped over the former with a transverse spacebetween each primary and the respective secondary coils through whichpasses a secondary core with an adjustable air gap. The construction issuch, that the secondary core is inductively interlinked with thesecondary coil or coils only. The present application is a continuationin part of the aforementioned application and affords a structure inwhich a portion of the primary core completes the magnetic path of thesecondary magnetic flux and vice versa. This results in substantialsavings in material and in a compactstructure of relatively small sizeand high efliciency.

The present invention has forits object to pro- /vide a transformer ofthe aforementioned type which is simple in construction, requires aminimum of'active material and is highly eflicient in operation.

Another object is to provide in a transformer having primary andsecondary windings magnetic cores affording paths for the primary andfor the secondary fluxes, so disposed that the reluctance of the primarymagnetic circuit is substantially unaffected by the adjustment of thereluctance of the secondary magnetic circuit.

Another object is to provide a unitary structure of a transformer havinga variable secondary reactance, including a secondary magnetic circuitwhich is inductively coupled with the secondary winding only, and thereluctance of which is adjustable without affecting the reluctance ofthe primary magnetic circuit.

Another object is to provide a high reactance transformer having primaryand secondary windings, a primary core inductively interlinked with theprimary and the secondary winding and a secondary core having a variablereluctance and interlinked with the secondary winding only.

Another object is to provide a unitary transformer and variable reactorwith a primary winding inductively mounted on the main magnetic frame ofsaid transformer and a secondary winding inductively interlinked withsaid main frame and also with a secondary magnetic frame provided with avariable air gap, each of said frames having a part which completes themagnetic path for the magnetic fiux induced in the other frame.

Other objects and advantages will hereinafter appear.

- The accompanying drawings are illustrative of several embodiments ofthe invention. In the drawings,

Fig. 1 is a vertical section of a single phase transformer embodying theinvention.

Fig. 2 is a top view and partially a cross-section along the lines 2-2of Fig. 1.

Fig. 3 is a side view of a modification of the magnetic frame shown inFigs. 1 and 2.

Fig. 4 is a vertical section of a modified detail of Fig. 3.

Fig. 5 is a section along the lines 5-5 of Fig. 4 and Fig. 6 is asection along the lines 6-6 of Fig. 4

Referring to the drawing, Figs. 1 and 2, the same illustrates a coretype transformer having a pair of primary windings l0 and H and acoordinated pair of secondary windings l2 and i3, telescoped over thecoils Ill and II, respectively. The transverse cross section of thecoils I D to [3, inclusive, is substantially rectangular and thetransverse space between the coils I0 and I2 and the coils II and I3,respectively, is increased on one side to provide for the passage of asecondary magnetic core or frame therethrough, as will appearhereinafter. The coils Ill and II are mounted on the vertical legs l4and I5 respectively, of a primary or main magnetic core or frame I6, thelower end of these legs being connected by a yoke IT. The legs I4 and I5 and the yoke I'I form a substantially U- shaped magnetic core orframe. The upper ends of the two legs [4 and 65 are provided withinturned polar extensions I8 and I9, respectively. The secondarymagnetic circuit comprises an inverted substantially U-shaped magneticcore or frame 20 having the legs 2i and 22, respectively, and a yoke 23.The transverse distance between the coils l0 and I2 and II and I3 issuch that the legs 2| and 22 of the secondary core can freely slidetherebetween. The distance between the polar extensions l8 and I9 isbridged by the yoke 23 of the secondary core. Thus the primary magneticcircuit includingthe core I! .is substantially closed, except for thenarrow gaps 24 and 25 between the polar extensions I8 and I9 and theyoke 23, which gaps are just sufficient re permit a free slidinglongitudinal movement of the secondary core within the primary core.

The secondary magnetic circuit is completed aeeaoar 3 through variableair gaps 26 and 21 between the yoke l1 and the legs 2| and 22,respectively. By moving the secondary core up and down within thesecondary coils, the length of these air gaps is varied, thus varyingthe reactance of the secondary magnetic circuit.

It will be noted that the primary windings iii and it which closelyembrace the legs it and [15, respectively, are only interlinked with thepri= mary magnetic circuit, while the secondary coils i2 and it whichembrace corresponding legs of both the primary and secondary core areinterlinked with both magnetic circuits. Thus by varying the air gaps 26and 2'5, the reactance oi the secondary circuit may be varied withoutvarying the reactance of the primary circuit. Fastened to the yoke 51and aligned with the legs 28 and 22, respectively, are fiat magnetic ornonmagnetic guide bars 28, which are straddled by the two halves of thesecondary core legs, so that one half of the laminations of said corelegs is arranged on each side of said guide bars 28 to slidelongitudinally thereon.

The guide bars 28 are provided with lateral extensions 29 adjacent tothe polar extensions i8 and I9, which extensions are inserted betweenthelaminations of the polar extension and riveted thereto. The secondarycore legs are provided with insulating bolts 30, the ends of which arethreaded and provided with nuts 3i and washers 32, interposed betweenthe nut or the bolt heads and the laminations to hold the lattertogether and to press them against the guide bars to permit movement ofthe secondary core relative to the primary core, to thereby vary the airgaps 26 and 21 between the respective parts of the secondary magneticcircuit.

To provide for adjustment of the air gap the secondary core yoke 23 hasafilxed thereto a tapped boss 34 and a similar tapped boss 35 is.afflxed to the yoke ll of the primary core. A threaded shaft 36provided with a hand wheel 31 engages the threads in the bosses 34 and35. The threads in the bosses 34 and 35 and on the corresponding partsof the shaft 36 are cut in I opposite directions, so that upon turningof the coils l2 and IS in the usual manner, the open circuit secondaryvoltage. It now the secondary coils are connected to an externalcircuit,

' as for instance a pair of welding electrodes, at

current flows in the secondary winding. This current generates a leakagemagnetic flux which passes through the leakage legs 2| and 22. Thisleakage magnetic flux is in opposition to the primary magnetic flux inthelegs l4 and I5, thus reducing the voltage induced in the secondarycoils. The current flowing in the secondary coils l2 and i3 as well theleakage magnetic flux in the legs 2| and 22 will increase to such anextent until the sumof the magnetic fluxes in the legs l4 and 2|respectively I and 22 induces a reduced voltage which corresponds to thewelding arc-voltage. The longer the air current which iiows in thesecondary coils i2 and it in order to get the required value of leakagemagnetic flux in the legs 2| and 22. On the other hand the open circuitsecondary voltage of the transformer is not substantially affected bythe length oi. the air gaps 25 and 21. By adjustment of the air gaps itis thus possible to adjust the welding current within very wide limits.

Fig. 3 illustrates a modification of the ma netic frame shown in Figs, 1and 2. The primary magnetic core 66 is similar to the core it of Fig. 1,except that the legs ii and d2 are not provided with intumed polarextensions. A secondary magnetic frame 413, corresponding to the frame2% of Fig. 2 has core legs as and Q5. which extend only partly throughthe interspaces between the primary and secondary coils. The yoke d5 ofthe primary core is provided with polar extensions d? and 48 which arein alignment with the legs db and d5, respectively, to form with thelatter variable air gaps 69 and 56, respectively, in the. secondarymagnetic circuit. The yoke 5| of the secondary magnetic frame 43 isprovided with lateral extensions 52 and 53 at its ends, to bridge themagnetic gap between the ends of the core legs it and t2, the latterbeing of such length that the reluctance of the air gaps 5d and 55between the extensions 52 and 53 and the core legs 4| and 42 is notaffected by the movement of the secondary frame 43. The air gaps 54 and55 are only sufficient to afford sliding movement between the respectiveparts and do not affect materially the reluctance of the primarymagnetic circuit.

In the modifications Figs. 4, 5 and 6, a number of the laminations inthe center of the core legs 4| and 42, are shortened to provide a slot56. A corresponding number of laminations of the yoke 5| are extended toform a tongue 51 which fits in the slot 56. The legs ti and 42 are eachfurther provided with an elongated hole 58 to afford free movement of athreaded bolt 55 which passes also through an elongated hole in thetonguev 51 of yoke 5| to afiord free movement of the latter. The bolt isprovided with nuts 6! at its ends and spring washers 62 are interposedbetween the nuts and the leg, to provide for resilient engagementtherebetween so as to compress the laminations and prevent vibration,while permitting relative movement between the primary and secondarycore.

Other modifications within the scope of the present invention andappended claims will be obvious to those skilled in the art.

What I claim as new and desire to by Letters Patent is:

l. A transformer providing for substantial variation of its secondaryreactance in response to variations of its secondary current,comprising, a first pair of legs and a first yoke to form therewith aunitary substantially U-shaped primary magnetic core, a second pair oflegs and a second yoke to form therewith a unitary substantiallyU-shaped secondary magnetic core, coplanar with an inverted relative tosaid primary core, said second yoke being-located and arranged toprovide a magnetic bridge between the open ends of said primary core,said first yoke providing a magnetic bridge including a pair of air gapsbetween the open ends of said secondary core, a pair of primary windingseach S ecure gaps 26 and 21 are adjusted, the greater is the encirclingone each of said first pair of legs and a pair of secondary windings,each secondary winding encircling one each of said first pair of legsand the corresponding one of said second pair of legs and having itsinner circumferential wall spaced from the outer circumferential wall ofthe respective primary winding to afiord pas sage therethrough of therespective leg or said secondary pair of legs.

2. A transformer providing for substantial variation of its secondaryreactance in response to variations of its secondary current,comprising, a first pair of legs and a first yoke to form therewith aunitary substantially U-shaped primary magnetic core, a second pair oflegs and a second yoke to form therewith a unitary substantiallyU-shaped secondary magnetic core coplanar with and inverted relative tosaid primary core, an intermediate portion of said secondary core beinglocated and arranged to provide a magnetic bridge between the open endsof said primary core, an intermediate portion of said primary coreproviding a magnetic bridge including a pair of air gaps between theopen ends of said secondary core, a pair of primary windings eachencircling one each of said first pair of legs and a pair of secondarywindings, each secondary winding encircling one each of said first pairof legs and the corresponding one of said second pair of legs and havingits inner circumferential wall spaced from the outer cir cumferentialwall of the respective primary winding to afford passage therethrough ofthe respective leg of said secondary pair of legs.

3. A transformer providing for substantial variation of its secondaryreactance in response to a variation of its secondary current,comprising, a first pair of legs and a first yoke to form therewith aunitary substantially U-shaped primary magnetic core, a second pair ofcore legs and a second yoke to form therewith a unitary substantiallyU-shaped secondary magnetic core inverted relative to and coplanar withand reciprocable within said primary core, said second yoke beinglocated and arranged between the open ends of said primary core toprovide with the latter a magnetic circuit of substantially constantreluctance for all relative positions of said cores, the intermediateportion of said first yoke providing a magnetic bridge including a pairof variable air gaps between the open ends of said secondary core, apair of primary windings each encircling one of said first pair of legs,and a pair of secondary windings, each secondary winding encircling oneof said first pair and the corresponding leg of said second pair of legsand having its inner circumferential wall spaced from the outercircumferential wall of the respective primary winding to afiord passagetherethrough of the respective leg of said secondary pair of legs.

4. A transformer providing for substantial variation of its secondaryreactance in response to a variation of its secondary current,comprising, a first pair of legs and a first yoke to form therewith aunitary substantially U-shaped primary magnetic core, a second pair ofcore legs and a second yoke to form therewith a unitary substantiallyU-shaped secondary magnetic core inverted relative to and coplanar withand reciprocable within said primary core, said second yoke beinglocated and arranged between the open ends of said primary core toprovide with the latter a magnetic circuit of substantially constantreluctance for all relative positions of said cores, the intermediateportion of said first yoke providing a magnetic bridge including a pairof variable air gaps between the open ends or said secondary core, apair of primary windings each encircling one each of said first pair orlegs, and a pair of secondary windings, each secondary windingencircling one each of said first pair of legs and the corresponding oneof said second pair of legs and having its inner circumferential wallspaced from the outer circumferential wall of the respective primarywinding to afiord passage therethrough of the respective leg of saidsecondary pair of legs.

5. A transformer providing for adjustment of its secondary reactance,comprising, a substantially U-shaped primary magnetic core having itspoles provided with inturned extensions, 9. coplanar substantiallyU-shaped secondary core reclprocable inside of and inverted relative tosaid primary core to provide a magnetic bridge of substantially constantreluctance between the polar extensions of said primary core for allrelative positions of said core and a. variable air gap between the endof each of the poles of said secondary core and the opposed intermediateportion of said primary core, a pair of primary windings each encirclingone of the legs of said primary core, and a pair of secondary windings,each secondary winding encircling one each of the legs of said primaryand the corresponding leg oi! said secondary core and having its innercircumferential wall spaced from the outer circumferential wall or therespective primary winding to afford passage therethrough of thecorresponding leg of said secondary magnetic core.

6. A transformer providing for substantial variation of its secondaryreactance in response to a variation of its secondary current,comprising, a first pair of legs, each having at one end thereof alateral polar extension and a first yoke connecting the other ends ofsaid legs to form therewith a unitary substantially U-shaped primarymagnetic core with said polar extensions extending towards the center ofsaid U, a second pair of core legs and a second yoke to form therewith aunitary substantially U-shaped secondary magnetic core inverted relativeto and coplanar with and reciprocable relative to said primary core,said second yoke being located and arranged to substantially close themagnetic gap between said polar extensions, said first yoke providing a.magnetic bridge including a pair of variable air gaps between the openends of said secondary core, a pair of primary windings each encirclingone each of said first pair or legs, a pair or secondary windings, eachsecondary winding encircling one each of said first pair of legs and thecorresponding one of said second pair of legs and having its innercircumferential wall spaced from the outer circumferential wall of therespective primary winding to afiord passage therethrough of therespective leg of said secondary pair of legs and means to reciprocatesaid cores relative to each other.

7. A transformer providing for substantial variation of its secondaryreactance in response to a variation of its secondary current,comprising, a primary laminated substantially U-shaped magnetic corehaving a first pair 01. legs and a. first yoke, a. secondary laminatedsubstantially U-shaped magnetic core coplanar with and inverted andreciprocable relative to said pri-.

mar core and having a. second pair or core legs and a. second yoke, saidsecond yoke being located and arranged between the open ends of saidprimary core to provide with the latter a magnetic circuit ofsubstantially constant reluctance for all relative positions or saidcores,

the intermediate portion of said first yoke providing a magnetic bridgeincluding a pair of variable air gaps between the open ends of saidsecondary core, a pair of primary windings each encircling one of saidfirst pair of legs and a pair of secondary windings, each secondarywinding encircling one of said first pair and the corresponding leg ofsaid second pair of legs and having its inner circumferential wallspaced from the outer circumferential wall of the respective primarywinding to afiord passage therethrough of the respective leg of saidsecondary pair of legs, said windings being mounted in fixed relation tosaid primary core, and means to reciprocate said cores relative to eachother. 7

8. A transformer providing for substantial variation of its secondaryreactance in response to a variation of its secondary current,comprising, a stationary primary laminated and sub-' stantially U-shapedlaminated magnetic core having a first pair of legs and a first yoke, asecondary laminated substantially U- shaped magnetic core coplanar withand inverted and reciprocable relative to said primary core and having asecond pair of core legs and a second,

yoke, said second yoke being located and arranged to provide a magneticbridge between the open ends of said primary core, said first yokeproviding a magnetic bridge including a pair of variable air gapsbetween the open ends of said secondary core, a pair of stationaryprimary windings each encircling one of said first pair of legs and apair of stationary secondary windings, each secondary winding encirclingone of said first pair and the corresponding leg of said second pair oflegs and having its inner circumferential wall spaced from the outercircumferential wall of the respective primary winding to afford passagetherethrough of the respective leg of said secondary pair of legs andmeans to reciprocate said secondary core.

9. A transformer providing for substantial variations of its secondaryreactance in response to a variation of its secondary current,comprising, a first pair of legs, an individual polar extension adjacentto one end of each of said legs and a first yoke connecting the otherends of said legs to form therewith a unitary substantially U-shapedprimary magnetic core, a second pair of core legs and a second yoke toform therewith a unitary substantially U-shaped secondary magnetic coreinverted relative to and coplanar with and reciprocable relative to saidprimary core, said second yoke being and said polar extensions beingaligned to substantially close the magnetic circuit of said primarymagnetic core, an inter- 5 mediate portion of said primary coreproviding a magnetic bridge including a pair of variable air gapsbetween the open ends of said secondary core, a pair of primary windingseach encircling one each of said first pair of legs, a pair of secondarywindings, each secondary winding encircling one each of said first pairof legs and the corre sponding one of said second pair of legs andhaving its inner circumferential wall spaced from the outercircumferential walls of the respective primary winding to affordpassage therethrough of the respective leg of said secondary pair oflegs and means to reciprocate said cores relative to each other.

10. A transformer providing for substantial variations of its secondaryreactance in response to a variation of its secondary current,comprising, a first pair of legs, an individual polar extension adjacentto one end of said legs and a first yoke connecting the other ends ofsaid legs to form therewith a unitary substantially U-shaped primarymagnetic core, a second pair of core legs and a second yoke to formtherewith a unitary substantially U-shaped secondary magnetic coreinverted relative to and coplanar with and reciprocablerelative to saidprimary core, said second yoke being provided at each end with a polarextension to substantially close the magnetic circuit between therespective free end of each of said primary cores and said second yoke,a polar extension for each of said second pair of legs attached to saidfirst yoke and aligned with the respective leg to provide with saidfirst yoke a magnetic bridge including a pair of variable air gapsbetween the free ends of said secondary core, a pair of primary windingseach encircling one each of said first pair of legs, a pair of secondarywindings, each secondary winding encircling one each of said first pairof legs and the corresponding one of said second pair of legs and havingits inner circumferential wall spaced from the outer circumferentialwalls' of the respective primary winding to afford passage therethroughof the respective leg of said secondary pair of legs and means'toreciprocate said cores relative to each other.

EDUARD FRIES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 851,743 gGehrkens Apr. 30, 19072,032,705 Klinkhamer Mar. 3, 1936 2,411,370 Fries Nov. 19, 1946

